Piezo actuators are known that have a base body, with a stack of stratified ceramic layers, and internal electrodes lying between them. The internal electrodes are made from a mixture of silver and palladium. The ceramic layers contain a ceramic based on lead zirconium titanate, which has a piezoelectric effect because of its ferroelectric properties. Because of the piezoelectric effect, the ceramic expands when electrical potential is present, so that it is possible to make actuators from such a multi-layer ceramic.
Also present in the known piezo actuators are outer electrodes, which are applied continuously to one lateral face of the base body and contact the internal electrodes.
In order to reduce the costs of producing the piezo actuators, an effort is made to replace the material of the internal electrodes and the material of the outer electrode with copper. In known piezo actuators, the outer electrode has the form of a continuous layer. This form of the outer electrode is not suitable for outer electrodes made of copper. Under thermal demands, which occur, for example, when contact elements are soldered onto the outer electrode, with a continuous layer there is a shearing force between the outer electrode and the base body of the piezo actuator, which leads to damage to the boundary layer between the outer electrode and the base body.
This damage to the boundary layer is accompanied by a reduction of the effective bonding area between the outer electrode and the base body.
A piezo actuator produced in this manner is subjected, in the course of its use, to a multitude of mechanical strains, which in turn lead to shearing forces between the base body and the outer electrode. Because of the relatively high strength of the copper electrode, these additional loads result in the damage that arises when the thermal load spreads across the surface of the boundary layer and leads to detachment of the outer electrode. Thus the piezo actuator fails and can no longer be used.